Abstract:

Methods and systems for continuity check of Ethernet multicast are
provided. A root MEP multicasts frames with continuity check function
information to all leaf MEPs in a multicast group, using a multicast DA.
The leaf MEP in a defect condition transmits a frame with defect
indication information to the root MEP. Responsive to receiving the frame
with defect indication information, the root MEP, using a unicast address
of the leaf MEP in a defect condition, transmits a frame with continuity
loss information only to the leaf MEP in a defect condition.

Claims:

1. A method for continuity check of Ethernet multicast, comprising the
steps of:multicasting frames with continuity check function information
from a root Maintenance Entity Group End Point (MEP) to all leaf MEPs in
a multicast group, using a multicast destination MAC address
(DA);transmitting a frame with defect indication information from a leaf
MEP in a defect condition to the root MEP; andresponsive to receiving the
frame with the defect indication information, the root MEP, using a
unicast address of the leaf MEP in a defect condition, transmitting a
frame with continuity loss information only to the leaf MEP in the defect
condition.

2. The method of claim 1, further comprising the step of:upon receiving
the frame with the defect indication information, the root MEP removing
the unicast address of the leaf MEP in the defect condition from the
multicast DA.

3. The method of claim 2, wherein said removing the unicast address from
the multicast DA is effectuated by making the leaf MEP in the defect
condition leave the multicast group.

4. The method of claim 2, further comprising the step of:after removing
the unicast address from the multicast DA, multicasting the frames with
the continuity check function information from the root MEP to all leaf
MEPs in the multicast group except the leaf MEP in the defect condition,
using the multicast DA.

5. The method of claim 1, wherein said multicasting is performed
periodically.

6. A system for continuity check of Ethernet multicast, comprising a root
Maintenance Entity Group End Point (MEP) and a plurality of leaf MEPs in
a multicast group, wherein the root MEP comprises:a transmitter,
configured to multicast frames with continuity check function information
to all of the plurality of leaf MEPs in the multicast group, using a
multicast destination MAC address (DA), and configured to transmit,
responsive to receiving a frame with defect indication information from a
leaf MEP in the multicast group, a frame with continuity loss information
only to the leaf MEP, using the unicast address of the leaf MEP; anda
receiver, configured to receive the frame with the defect indication
information from the leaf MEP in a defect condition; andthe leaf MEP
comprises:a transmitter configured to transmit a frame with the defect
indication information to the root MEP, upon detecting the defect
condition; anda receiver configured to receive the frames with the
continuity check function information with the multicast DA and the frame
with the continuity loss information with its own unicast address, from
the transmitter of the root MEP.

7. The system of claim 6, wherein the root MEP further comprises:means for
removing a unicast address of a leaf MEP from the multicast DA, upon
receive a frame with the defect indication information from the leaf MEP.

8. The system of claim 7, wherein the means for removing the unicast
address from the multicast DA is configure to remove the unicast address
from the multicast DA by making the leaf MEP leave the multicast group.

9. The system of claim 6, wherein the transmitter of the root MEP is
further configured to,after removing the unicast address from the
multicast DA, multicast frames with the continuity check function
information to all leaf MEPs in the multicast group except the leaf MEP
from which the frame with the defect indication information is
transmitted, by using the multicast DA.

10. The system of claim 6, wherein the transmitter of the root MEP is
configured to multicast the frames with the continuity check function
information periodically.

Description:

BACKGROUND OF THE INVENTION

[0001]1. Field of the Invention

[0002]The present invention general relates to a multicast Ethernet OAM
(Operating Administration and Maintenance) mechanism, and more
particularly to a method and system for continuity check of Ethernet
multicast.

[0003]2. Description of the Related Art

[0004]With the rapidly expanding deployment of Ethernet, there is an
increasing demand for Ethernet OAM functionality. Various standards are
being developed that aim to provide advanced OAM capabilities (also
referred to as Ethernet Connectivity and Fault Management or Ethernet
CFM). In particular, two standards, IEEE 802. 1ag and ITU-T Y.1731,
incorporated by reference herein, have defined the mechanism for OAM
functionality in Ethernet networks, especially point-to-point (i.e.
unicast) Ethernet OAM. In the context of ITU-T.Y.1731, an end point of an
Ethernet MEG (Maintenance Entity Group) is called a "MEG End Point" or
MEP. The MEP are used by system administrators to initiate and monitor
OAM activity (by issuing appropriate OAM frames).

[0005]Ethernet continuity check function is used for proactive OAM. It is
used to detect loss of continuity (LOC) between any pair of MEPs in a MEG
and other defect conditions, such as mismerge, unexpected MEP, unexpected
MEG Level, unexpected period, etc. The process of continuity check for a
point-to-point connection is shown in FIG. 1. In the process, a CCM
(Continuity Check Message) with RDI (Remote defect indication) bit being
0, is sent periodically from one MEP (e.g. MEP 101 in FIG. 1) to another
MEP (e.g. MEP 102 in FIG. 1), step 110. If the link between the two MEPs
is suffered, for example by SF (signal fail) or SD (signal degradation),
MEP 102 will send back RDI to MEP 101, to indicate a fault for receiving
the CCM, step 120. When MEP 101 received RDI, it enters into RDI defect
status, and sends CCM with RDI bit being 1 to MEP 102, to indicate that
there is something wrong on the link between them, step 130.

[0006]CCM and RDI are the most important elements to check and monitor the
continuity. The format of CCM message used by a MEP is shown in FIG. 2.
"MEL" (MEG Level) is used to identify MEG Level of OAM PDU. "Version" is
used to identify the OAM protocol version which is always 0. "OpCode" is
used to identify the type of the remaining content, and the value of
OpCode for CCM is 1. "Flag" is used for RDI and other information needed
by CCM in continuity check. "TLV Offset" contains the offset to the first
TLV in an OAM PDU relative to the TLV Offset field and is set to 70 for
CCM. "Sequence Number" is set to all-ZEROes for this Recommendation. "MEP
ID" is used to identify the MEP transmitting the CCM frame and is unique
within the MEG. "MEG ID" is used to identify the MEG to which the MEP
transmitting the CCM frame belongs. Each of "TxFCf", "TxFCb", "RxFCb" is
4-octet integer values with samples of the wrap-around frame counters.
"Reserved" fields are set to all-ZEROes. "End TLV" is an all-ZEROes octet
value.

[0007]As a format of the field "Flag" shown in FIG. 3, RDI is indicated by
the first bit of the field "Flag". If the bit is 1, it indicates there is
something wrong on the link, otherwise it is 0. "Period" contains the
value of the CCM transmission period configured at the MEP 101
transmitting the CCM frame. The value of the field "Period" can be "000",
which means the CCM message is not transmitted periodically.

[0008]In the unicast scenario, the continuity check can be implemented in
a relatively straightforward manner, through the continuity check process
for a point-to-point connection described above. However, problems will
occur in the multicast scenario, i.e. point-to-multipoint. In the
multicast scenario, when the root MEP receive the RDI from a MEP in a
defect condition which belongs to a multicast group, it will send all of
the leaf MEPs in the multicast group a CCM message with RDI bit being 1.
That will cause the system administrators to consider that all of the
connections from root MEP to the leaf MEPs are down, and will in turn
result in that all of the leaf MEPs consider that the connections between
them and the root MEP are down, and then all of the leaf MEPs are
disabled to transmit data through the connections. In other words, the
problem is that the connections between the root MEP and the leaf MEPs
which are not in a defect condition will be interrupted by the leaf MEP
in a defect condition.

[0009]Now the commonly used solution for continuity check in multicast
scenario is to use a group of a point-to-point continuity check, to
verify the continuity of each connection between the root MEP and
respective leaf MEP. In the continuity check process, the CCM is
addressed to corresponding leaf MEP with the unicast DA (Destination MAC
Address) of the leaf MEP. The unicast address of the unicast DA
identifying the MEP uniquely in the multicast group doses not depend on
the branching mechanism. Therefore, The continuity check mechanism is
independent among all the leaf MEPs. It is a good method to check the
continuity. However, the use of a point-to-point continuity check for
each connection is inefficient and undermines the purpose of multicast in
the first place--the goal of greater useable bandwidth and associated
higher processing efficiency.

[0010]Thus, it would be an advancement in the art to provide methods and
systems that allow for simpler and more efficient continuity check of
Ethernet multicast, and that overcome the above limitations and
disadvantages.

SUMMARY OF THE INVENTION

[0011]The following presents a simplified summary of the invention in
order to provide a basic understanding of some aspects of the invention.
This summary is not an extensive overview of the invention. It is not
intended to identify key or critical elements of the invention or to
delineate the scope of the invention. The following summary merely
presents some concepts of the invention in a simplified form as a prelude
to the more detailed description provided below.

[0012]To overcome limitations in the prior art described above, and to
overcome other limitations that will be apparent upon reading and
understanding the present specification, the present invention is
directed to methods and systems for continuity check of Ethernet
multicast.

[0013]In an embodiment of the present invention, a method for continuity
check of Ethernet multicast comprises multicasting frames with continuity
check function information from a root MEP to all leaf MEPs in a
multicast group, using a multicast DA; transmitting a frame with defect
indication information from a leaf MEP in a defect condition to the root
MEP; and responsive to receiving the frame with defect indication
information, the root MEP, using a unicast address of the leaf MEP in a
defect condition, transmitting a frame with continuity loss information
only to the leaf MEP in a defect condition.

[0014]In another embodiment of the present invention, the method further
comprises, upon receiving the frame with defect indication information,
the root MEP removing the unicast address of the leaf MEP in a defect
condition from the multicast DA.

[0015]In another embodiment of the present invention, the method further
comprises, after removing the unicast address from the multicast DA,
multicasting the frames with continuity check function information as
before from the root MEP to all leaf MEPs in the multicast group except
the leaf MEP in a defect condition, using the multicast DA.

[0016]In an embodiment of the present invention, a system for continuity
check of Ethernet multicast, comprising a root MEP and a plurality of
leaf MEPs in a multicast group. The root MEP comprises a transmitter,
configured to multicast frames with continuity check function information
to all of the plurality of leaf MEPs in the multicast group, using a
multicast DA, and configured to transmit, responsive to receiving a frame
with defect indication information from a leaf MEP in the multicast
group, a frame with continuity loss information only to the leaf MEP,
using the unicast address of the leaf MEP; and a receiver, configured to
receive the frame with defect indication information from the leaf MEP in
a defect condition. The leaf MEP comprises a transmitter configured to
transmit a frame with defect indication information to the root MEP, upon
detecting a defect condition; and a receiver configured to receive the
frames with continuity check function information with the multicast DA
and the frame with continuity loss information with its own unicast
address, from the transmitter of the root MEP.

[0017]With the solution of the present invention, it is efficient to
perform the continuity check through multicast. Furthermore, it is simple
than the prior art in which a group of a point-to-point continuity check
is utilized. At the same time, through the present invention, the
connection between the root MEP and the leaf MEP in a defect condition
will not interrupt the other connections between the other leaf MEPs that
are not in a defect condition and the root MEP. Additionally, the
compatibility with the existed OAM specifications can be preserved.

[0018]Those skilled in the art will appreciate that the above is merely an
introduction to the subject matter described in more detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]The present invention may be better understood, and its numerous
objects, features, and advantages made apparent to those skilled in the
art by referring the accompanying drawings, wherein

[0020]FIG. 1 schematically illustrates a process of continuity check for a
point-to-point connection in the prior art;

[0021]FIG. 2 illustrates a standardized format of CCM message;

[0022]FIG. 3 illustrates a standardized format of RDI;

[0023]FIG. 4 shows a schematic functional block of the system for
continuity check of Ethernet multicast in accordance with an embodiment
of the present invention;

[0024]FIG. 5 is a sequence diagram illustrating a method for continuity
check of Ethernet multicast in accordance with an embodiment of the
present invention; and

[0025]FIG. 6 is a flow chart illustrating a further method for continuity
check of Ethernet multicast in accordance with another embodiment of the
present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0026]In the following description of the various illustrative
embodiments, reference is made to the accompanying drawings, which form a
part hereof, and in which are shown by way of illustration various
exemplary embodiments in which the invention may be practiced. It is to
be understood that other embodiments may be utilized and structural and
functional modifications may be made without departing from the scope of
the present invention.

[0027]FIG. 4 shows a schematic functional block of an Ethernet multicast
system in which the present invention can be implemented. The structure
and functions of such an Ethernet multicast system and those of the
associated network elements are only described when relevant to the
invention.

[0028]The system 400, according to an exemplary embodiment, comprises a
plurality of leaf MEPs 420, 430, and 440, and a root MEP 410. The root
MEP 410 can multicast data to all of the leaf MEPs which belong to a MEP
group, thereby advantageously saving bandwidth resources from the root to
the leaf if more than two leaf MEPs are to be transmitted to.

[0029]The root MEP 410 comprises transmitter 411 and receiver 412, which
are used for transmitting or receiving frames for the continuity check
process to or from leaf MEPs 420, 430, and 440, respectively. The basic
structure and operation of transmitter 411 and receiver 412 are known to
one skilled in the art and only the details relevant to the present
solution are discussed in detail. Root MEP 410 further comprises means
413, which is coupled to transmitter 411 and receiver 412 and used for
managing the continuity check of Ethernet multicast. The functions of
means 413 may be implemented with a digital signal processor, memory, and
computer programs for executing computer processes.

[0030]Each of leaf MEPs 420, 430, 440, comprises transmitter 421, 431, 441
and receiver 422, 432, 442 respectively, which are used for transmitting
or receiving frames for the continuity check process to or from root MEP
410. The basic structure and operation of transmitter 422, 432, 442 and
receiver 422, 432, 442 are known to one skilled in the art and only the
details relevant to the present solution are discussed in detail.

[0031]Now a description of the process of continuity check of Ethernet
multicast in accordance with an embodiment of the present invention is
made referred to FIG. 5. The process can be initiated by system
administrator manually or automatically. The structures and functions of
a root MEP 501, and leaf MEP 502, 503, 504, are the same to the
corresponding elements (root MEP 410, and leaf MEP 420, 430, 440) in
system 400 illustrated in FIG. 4.

[0032]In step 510, root MEP 501 multicasts frames with continuity check
information, i.e. frames carrying CCM message which are called CCM
frames, to all of the leaf MEPs 502, 503, 504 in a multicast group.
Preferably, the CCM frames can be transmitted periodically and the period
can be set in the related bits as described with reference to FIG. 3. The
multicast mechanism is similar to the normal multicast in Ethernet
network. The simplified format of the CCM frame is illustrated as block
511 above the arrows that denotes step 510, wherein the RDI bit is 0. The
CCM frames 511 are addressed to all of the leaf MEPs with a multicast DA
of the multicast group.

[0033]When leaf MEP 502 in the multicast group has encountered a defect
condition, for example, leaf MEP 502 have not received the CCM frames 511
in 3.5 period, it will transmit a frame with defect indication
information to root MEP 501, as shown in step 520. The frame is
preferably a CCM frame, wherein the RDI bit is set to 1 by leaf MEP 502,
to indicate that the continuity between leaf MEP 502 and root MEP 501 is
a in defect condition. The simplified format of the CCM frame is
illustrated as block 521 above the arrow that denotes step 520, wherein
the unicast address of leaf MEP 502 is provided in the field "Source".

[0034]In step 530, responsive to receiving the CCM frame with RDI=1 from
leaf MEP 502, root MEP 501 will transmit a frame with continuity loss
information to leaf MEP 502, to confirm the continuity between root MEP
501 and leaf MEP 502 has been lost. The frame is preferably a CCM frame,
wherein the RDI bit is 1. The simplified format of the CCM frame is
illustrated as block 531 above the arrow that denotes step 530. CCM frame
531 is addressed only to leaf MEP 502 with the unicast address of leaf
MEP 502 and the other leaf MEPs 503, 504 would not receive CCM frame 531.

[0036]As can be appreciated to one skilled in the art, root MEP 501 and
leaf MEPs 502, 503, and 504 are illustrative, and the leaf MEP in a
defect condition can be any of the leaf MEPs in the multicast group. The
number of leaf MEPs in a defect condition is not limited to one, but any
possible number.

[0037]FIG. 6 is a flow chart illustrating a further method for continuity
check of Ethernet multicast in accordance with another embodiment of the
present invention. In the process shown in FIG. 6, the steps 610, 620 and
640 are similar to the corresponding steps 510-530 illustrated in FIG. 5.
The difference lies in that, upon receiving the frame with defect
indication information, root MEP 501 can remove the unicast address of
leaf MEP 502 in a defect condition from the multicast DA. For example,
means 413 in the root MEP can extract the unicast address and remove it
from a list about the mapping between the unicast addresses of the leaf
MEPs in the multicast group and the multicast DA. Preferably, the
removing can be achieved through making the leaf MEP in a defect
condition leave the multicast group. A more detailed description of the
removing is provided in IETF RFC4604-IGMP (Internet Group Management
Protocol), entitled "Using Internet Group Management Protocol Version 3
(IGMPv3) and Multicast Listener Discovery Protocol Version 2 (MLDv2) for
Source-Specific Multicast," and IEEE802.1d-2004--Chapter 10-GMRP(GARP
multicast register protocol), entitled "Media Access Control (MAC)
bridge", which are incorporated herein by reference in its entirety.

[0038]The process can further comprises step 650, which is preformed after
step 630. In step 650, after removing the unicast address from the
multicast DA, root MEP 501 continue to multicast the frames with
continuity check function information as before, i.e. as in step 610, to
all leaf MEPs 503, 504 in the multicast group except leaf MEP 502, using
the multicast DA. Since the unicast address has been removed from the
multicast DA, the MEP 502 would not receive the frames multicasted using
the multicast DA. Step 650 may or may not occur at the same time with
step 640. Step 650 may occur before or after step 640, depending on the
settings in root MEP 501.

[0039]One or more aspects of the invention may be embodied in
computer-executable instructions, such as in one or more program modules,
executed by one or more computers or other devices. Generally, program
modules include routines, programs, objects, components, data structures,
etc. that perform method steps of the invention when executed by a
processor in a computer or other device. The computer executable
instructions may be stored on a computer readable medium such as a hard
disk, optical disk, removable storage media, solid state memory, RAM,
etc. As will be appreciated by those skilled in the art, the
functionality of the program modules may be combined or distributed as
desired in various embodiments. In addition, the functionality may be
embodied in whole or in part in firmware or hardware equivalents such as
integrated circuits, field programmable gate arrays (FPGA), and the like.

[0040]Although the invention has been described with reference to specific
embodiments, this description is not mean to be constructed in a limited
sense. Various modifications of the disclosed embodiments, as well as
alternative embodiments of the invention, will become apparent to persons
skilled in the art upon reference to the description of the invention. It
is, therefore, contemplated that the appended claims will cover such
modifications that fall within the scope of the invention, or their
equivalents.